1. Technical Field
Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
The fixing device may include a fixing rotary body, such as a roller, a belt, and a film, and a pressing rotary body, such as a roller and a belt, pressed against the fixing rotary body to form a fixing nip therebetween through which a recording medium bearing an unfixed toner image is conveyed. As the recording medium is conveyed through the fixing nip, the fixing rotary body heated by a heater and the pressing rotary body apply heat and pressure to the recording medium, fixing the toner image on the recording medium.
The fixing device is requested to shorten a warm-up time taken to heat the fixing device from an ambient temperature to a desired fixing temperature to fix the toner image on the recording medium after the image forming apparatus is powered on. The fixing device is also requested to shorten a first print time taken to output a recording medium bearing a fixed toner image onto an outside of the image forming apparatus after the image forming apparatus receives a print job.
To address those requests, the fixing device may employ a ceramic heater disposed opposite the fixing rotary body at the fixing nip. However, since the ceramic heater heats the fixing rotary body at the fixing nip, the fixing rotary body has a decreased temperature at an entry to the fixing nip situated upstream from the ceramic heater in a rotation direction of the fixing rotary body, resulting faulty fixing.
On the other hand, since the image forming apparatus is requested to print quickly, an increased number of recording media is conveyed through the fixing device per minute. Accordingly, the fixing device requires an increased amount of heat to be supplied to the recording media. Consequently, upon start of a print job for printing on a plurality of recording media continuously, the fixing device may suffer from shortage of heat.
To address those circumstances, a fixing device 80R shown in FIG. 1 is proposed by JP-4818826-B2 (JP-2007-334205-A). FIG. 1 is a schematic vertical sectional view of the fixing device 80R.
As shown in FIG. 1, the fixing device 80R includes an endless belt 201 rotatable counterclockwise in FIG. 1; a tubular, metal thermal conductor 202 stationarily disposed inside the endless belt 201 to guide the endless belt 201; a heater 203 situated inside the metal thermal conductor 202 to heat the endless belt 201 through the metal thermal conductor 202; and a pressure roller 204 pressed against the metal thermal conductor 202 via the endless belt 201 to form a fixing nip 207 between the endless belt 201 and the pressure roller 204. As the pressure roller 204 rotates clockwise in FIG. 1, the endless belt 201 rotates counterclockwise in FIG. 1 in accordance with rotation of the pressure roller 204. The metal thermal conductor 202 heated by the heater 203 in turn heats the endless belt 201 entirely, shortening the first print time and overcoming shortage of heat. Alternatively, the metal thermal conductor 202 may be eliminated to allow the heater 203 to heat the endless belt 201 directly.
However, since heat from the heater 203 is concentrated on the endless belt 201, peripheral components other than the endless belt 201 may be heated slowly and therefore susceptible to condensation. For example, condensation occurs on a separator disposed downstream from the fixing nip 207 in a recording medium conveyance direction D1 to separate a recording medium S from the endless belt 201. If condensation occurs, as the recording medium S is conveyed over the separator, droplets may adhere from the separator to the recording medium S, damaging the toner image on the recording medium S.